This invention provides an enhanced wet rotor electric motor, where the rotor magnets are subject to highly corrosive wet conditions.
In wet rotor motors, such as for centrifugal pumps, the use of the desirable soft-iron ‘back-iron’ becomes problematic, due to the corrosivity of the operating environment. Without such soft iron magnetic material the power output for a given electrical input to the stator coils is reduced.
It is well-known to design a brushless DC motor (“BLDC”) having permanent magnets on the rotor and a fixed stator armature having electronic switches to change polarity, thus avoiding the problems created by requiring brushes to connect electric current to a moving electromagnetic armature. In the BLDC motor, generally, an electronic controller replaces the brushes used for commutation in the more common DC electric motor, for continually switching the phase of electric power to the windings by switching the polarity of the electric power presented to the motor via the stator. The BLDC motors provide more torque per weight and per watt of power input; they have greater reliability and durability, because there are no brushes to be worn, and reduced noise. Similarly, by elimination of the brush or commutator, there are no ionizing sparks which create electromagnetic interference and also further wear the parts. Furthermore, the stator windings, being stationary, can be cooled by conduction, which eliminates the need for air flow inside the motor and thus allows for entirely enclosing the motor to protect it from dirt or other foreign material.
Prior BLDC's have been designed and manufactured using permanent there the lines of North-South polarity run parallel to the rotor axis. One of the problems of controlling a brushless motor is that the electronic system must be aware of the location of the rotor magnets. The use of axially extending magnets render that determination very difficult and require sophisticated electronic sensors. It has also been known to use rare earth magnets arranged in a ring for specific uses requiring extremely high flux density, such as in wind turbine generators and in controls for high energy particle accelerators for pure physics research.